Resistance core ignition cable



Nov. 5, 1963 R' H' PUBLow Filed Aug. 4, 1961 RESISTANCE CORE IGNITION CABLE lIVVENTOR. RICHARD H. PUBLow AGENT United States Patent O 3,109,881 RESISTANCE CORE IGNITIGN CABLE Richard H. Publow, Marion, Ind., assigner to Essex Wire Corporation, Fort Wayne, Ind., a corporation of Michigan Fiied Aug. 4, 1961, Ser. No. 129,265 1 Claim. (Cl. 174-118) This invention relates to electric cable for internal combustion engine ignition systems and particularly to such cable having a conductive core of high resistance for suppressing the generation of high frequency interference Eby the ignition system.

isfactory and commercially successful, it is not lideal because lthe resi-stance of the core changes substantially during eXtr-uding and vulcanization of the cable sheath. In addition, the tensile strength of the core drops by as muchas `fifty (50) percent during vulcanization of the sheath. Also, considerable difiiculty has been experienced in making goo-d electrical connection of terminals to this cable. All these have contributed to a high scrap loss and a corresponding high cost in the use of the cable.

When a terminal connection is made tothe cable shown in the Wolcott patent by means of a wire clip or pin driven into the core,`it has been found Vthat a significant number of cables willv fail after ra short period of use. Investigation of these failures revealed that their prevention depends upon the wire pin of the terminal being driven accurately into the core to provide good contact between the core and the pin along the entire length of the latter. At times, `due to the core'not being exactly centered in the sheath or the wire pin being deformed, only a small part of the wire pin will make contact with the cable core. A resistance check of the cable assembly will not reveal this faulty contact, but later, when the assembly is employed in a vehicle engine, a high-resistance connection develops, due to the small amount of contact. The high-resistance connection overheats, causing partial deterioration of the rayon and linen core which results in deposit of gurnmy matter on the surface of the terminal pin. This further increases the resistance of the connection, until there is no contact between the wire pin and the graphite on the core. Then sparking occurs between the terminal pin and the nearest conductive portion of the core, which causes burning and destruction of the core. After a time, so much of the core is destroyed that further sparking cannot occur and the cable is cornpletely inoperative. Such failures of defective connections may be reproduced in only a few minutes by an accelerated test, in which 11G-volt, Gti-cycle voltage is applied to a short length of cable.

Another difficulty experienced with cable constructed according to the Wolcott patent is that, when it is subjected to a ysevere pulling force, as during its disconnection from a spark plug, its resistance will increase. Upon termination of the stress, the resistance value of the cable does not return to its original value, but remains with a substantial permanent increase.

It will be evident from the foregoing that manufacturing and field experience with resistance core ignition cable has demonstrated a need for further improvement to provide a cable with stable electrical properties and increased reliability under adverse operating conditions.

An object of the present invention is to provide an improved resistance core cable for electrical ignition systems and the like, characterized lby a high stability in electrical characteristics -under adverse manufacturing and operating conditions.

Another object of this invention is to provide such resistance core cable having a high degree of reliability under operating conditions.

A further object of this invention is to provide an iniproved resistance core cable which may be economically and conveniently manufactured.

Other objects and advantages of the invention will become apparent upon consideration of the following specification taken in conjunction with the accompanying drawing in which:

FIG. l is a perspective View illustrating one type of cable constructed in accordance with the teachings of this invention, some parts of the cable being partially cut away in order to clearly illustrate other parts which would not normally be visible; and

FIG. 2 is an enlarged perspective View, partly broken away and in section, of a glass fiber employed in the cable.

Referring to the drawing, a resistance core cable is shown comprising an outer insulating sheath 16; an inner insulating sheath 11, a braided envelope 12 of mineral fibers, and a fibrous mineral base conductive core 13. The outer sheath 10 is preferably of an oiland ozoneresistant elastomeric material, such as a polychloroprene compound elastomer. The inner sheath may consist of a butadiene-styrene rubber. Other known flexible elastomers of any suitable types may also be used with satisfactory results and for some purposes, only a single sheath may be employed. Each of the sheaths is applied over the envelope 12 by a conventional extrusion process and cured in a well-known Imanner with the sheaths bonded to each other and the inner sheath '11 adhering to the envelope 12.

The core 13 consists of a large number of glass liber filaments 14 which are arranged lengthwise of the cable yand are substantially continuous in length throughout any given length of the cable. Each of the filaments 14 is composed of a number of substantially continuous and nontwisted glass fibers 15 in compact, side-by-side relation. Each fiber 15 throughout its length has on its surface a pliant, tenaciously adhering ill-m or coating 16 of electrically conducting material. This continuous unitary film may consist of finely divided for colloidal carbon particles and a binder of flexible or elastic material which holds the carbon particles to the -fibers 15. Film 16 may be one of the materials Idisclosed in United States Patents 1,771,055 and 2,495,199, or it may be la homogenous coating of the type disclosed in United States Patent 2,341,219. Any method conventionally employed for applying such films and coatings to a glass fiber may be utilized to form coating y1&5 on the fibers v15.

A preferred construction uses 60 filaments 14- gathered together, preferably in substantially parallel form, although they rnay be twisted to some extent. Each filament 14 consists of 204 glass fibers of .00036-inch diameter. The tubular envelope 12 is formed tightly about the core 13 by a suitable l-carrier braiding machine. The preferred envelope construction comprises strands 117 closely woven with 18.2 picks per inch over the lcore 13 in a basket-weave braid or standard two-over-and-two-under braid. The strands 17 are each composed of four parallel filaments ea-ch consisting of 20=4 glass fibers .00036 inch in diameter which have no conductive coating. The fibers comprising the strands 17 are substantially continuous in length throughout any given length of the cable and are not appreciably twisted.

The utilization of a core lhaving glass ibers with individual tenacious coatings of lmlike, conductive material, as opposed to a core impregnated with unfixed carbon particles, nas the advantage that it provides a cable with considerable more stability in resistance value when the cable is axially stretched. Because the envelope 12 is mechanically connected with the sheaths l `and 11 and initially sustains axial tensile stresses `applied to the cable while the fibers 14 remain relatively unstressed, there is little stressing of the conductive material. Further, the envelope, by virtue of its basket-weave construcy tic-n, exerts a radial compressive force upon the core in response to a strong axial pull which compacts the coated laments into a better conducting relation with each other. Surprisingly, it has been found that these features cause the'resistance of cable constructed according to this invention to decrease by `as much as twenty-five (25%) percent upon a sever axial pull, instead of increasing. Upon termination of the pull, the resistance of the cable returns to substantially its initial value, whereas, cable constructed according to the above-mentioned Wolcott patent has a substantial permanent increase `in resistance when subjected to the same force.

It has also been found that the electrical connection properties of cable constructed according to the present invention are vastly superior to that of the prior construction described above. Using the accelerated test described above, a properly terminated cable of the latter prior type fails in about twenty minutes, its resistance increasing to six (6) times its initial value. The present cable, when subjected to the same test, merely decreased slightly in resistance. Then, to determine if the present cable could be satisfactorily terminated, even if a wire pin terminal had a minimum Contact with the conductive core of the cable, two (2) spaced, 1/32-incl1- diameter pins were inserted radially into the cable sheath until they penetrated the cable core. Although this amounted to only ve (5%) percent of the normal contact between the pins and the core, there was no failure of the core when the pins were connected'to a 11G-volt, Gti-cycle voltage, even when left energized until smoke came from the cable and the jacket swelled. The resistance of the heated cable was about twenty-live (25%) percent less than its initial cool valu-e, but upon cooling returned to substantially its normal value. The same specimen was subjected to two more cycles of the same test, with identical results. It will be evident from the foregoing that a surprisingly successful solution of the termination problem has been attained by the present invention.

It will be understood that modications and variations may be effected without departing from the scope of the invention as claimed.

- v What is claimed is:

An electrical resistance cable comprising:

(a) an electrically conductive core consisting of thousands of substantially straight and parallel ilexible glass fibers individually coated with :a continuous film of conductive material disposed in adherent relationship over the peripheral surface of each ber; said ilrn containing minute particles of carbon and a binder material which tenaciously binds said carbon particles to said fiber so that each fiber is essentially free of unixed carbon particles;

(b) an envelope substantially free of any electrically conductive material surrounding said core and comprising a tubular braid of closely-woven strands,.each `strand consisting of a plurality of substantially continuous glass ibers in substantially parallel relationship; said envelope being longitudinally extensible in response to axial pulling forces to exert a compressive force upon said core; and

(c) an outer insulating sheath of elastomeric material surrounding and adhering to said envelope.

References Cited in the iile of this patent UNITED STATES PATENTS 

